Use of a succinimide compound as an anti-corrosion additive in a lubricant composition for a propulsion system of an electric or hybrid vehicle

ABSTRACT

The invention relates to the use of at least one succinimide compound as an anti-corrosion additive in a lubricant composition for a propulsion system of an electric or hybrid vehicle, said lubricant composition comprising one or more amino and/or sulfur anti-wear additives. The invention also relates to the use of a lubricant composition for lubricating a propulsion system of an electric or hybrid vehicle.

The present invention relates to the field of lubricant compositions fora propulsion system of an electric or hybrid vehicle. The invention moreparticularly relates to the use of succinimide compounds for improvingthe anticorrosion properties of a lubricant composition incorporatingone or more amine-based and/or sulfur-based antiwear additives.

TECHNICAL FIELD

The changes in the international standards for the reduction of CO₂emissions, but also for the reduction of energy consumption, has drivenmotor vehicle constructors toward proposing alternative solutions tocombustion engines.

One of the solutions identified by motor vehicle constructors consistsin replacing combustion engines with electric motors. The research aimedat reducing CO₂ emissions has thus led to the development of electricvehicles by a certain number of motor vehicle companies.

For the purposes of the present invention, the term “electric vehicle”denotes a vehicle comprising an electric motor as sole means ofpropulsion, as opposed to a hybrid vehicle which comprises a combustionengine and an electric motor as combined means of propulsion.

For the purposes of the present invention, the term “propulsion system”denotes a system comprising the mechanical parts required for propellingan electric vehicle. The propulsion system thus more particularlyencompasses an electric motor or the rotor-stator assembly of the powerelectronics (dedicated to regulating the speed), a transmission and abattery.

In general, it is necessary to use, in electric or hybrid vehicles,lubricant compositions, also known as “lubricants”, for the mainpurposes of reducing the friction forces between the various parts ofthe propulsion system of the vehicle, notably between the metal parts inmotion in the motors. These lubricant compositions are also effectivefor preventing premature wear or even damage of these parts, and inparticular of their surface.

To do this, a lubricant composition is conventionally composed of one ormore base oils which are generally combined with several additivesintended for stimulating the lubricant performance of the base oil, forinstance friction-modifying additives, but also for affording additionalperformance.

In particular, “antiwear” additives are considered in order to reducethe wear of the mechanical parts of the motor, and thus to preventdegradation of the durability of the motor.

A wide variety of antiwear additives exists, among which mention may bemade, for example, of dimercaptothiadiazoles, polysulfides, notablysulfur-based olefins, amine phosphates, or else phospho-sulfuradditives, for instance metal alkylthiophosphates, in particular zincalkylthiophosphates and more specifically zinc dialkyldithiophosphatesor ZnDTP.

Among these antiwear additives, the ones that are notably favored areamine-based and/or sulfur-based antiwear agents, such asdimercaptothiadiazoles, zinc dithiophosphate or polysulfides.

Unfortunately, these amine-based and/or sulfur-based antiwear additives,such as dimercaptothiadiazoles, have the drawback of being corrosive.The problem of corrosion is particularly critical in electric propulsionsystems. In particular, corrosion can lead to a risk of deterioration ofthe stator and rotor windings, the sensors in the propulsion system, thesolenoid valves in the hydraulic system, but also of the rollingbearings between the rotor and stator of an electric motor, which aregenerally copper-based and thus particularly susceptible to corrosion,or to the seals or varnishes in the propulsion system.

In addition, in order to be able to cool the propulsion systems ofelectric or hybrid vehicles, it is essential that the lubricant beinsulating in order to avoid any failure in the electrical components.In particular, a conductive lubricant can lead to a risk of electricalcurrent leakage in the stator and rotor windings, which thus reduces theefficiency of the propulsion systems, and creates possible overheatingof the electrical components, even to the point of damaging the system.In the context of using lubricants for electric or hybrid vehiclepowertrain systems, it is thus crucial for the lubricants to have good“electrical” properties in addition to non-corrosive properties.

The present invention is directed, specifically, towards overcoming thisdrawback.

SUMMARY OF THE INVENTION

More precisely, the present invention relates to the use of at least onesuccinimide compound, as an anticorrosion additive in a lubricantcomposition intended for a propulsion system of an electric or hybridvehicle and comprising one or more amine-based and/or sulfur-basedantiwear additives.

Succinimide compounds, for instance polyalkylene succinimides such aspolyisobutylene succinimides (PIBSI), have already been proposed asdispersants, for example in lubricants for vehicle motors, as described,for example, in patent application WO 2014/096 328.

To the inventors' knowledge, it has, however, never been proposed to usesuccinimide compounds as anticorrosion additives in the context of usinga lubricant for a propulsion system of an electric or hybrid vehicle, toovercome the corrosion effects brought about by the use of amine-basedand/or sulfur-based antiwear additives.

Surprisingly, as illustrated in the example that follows, the inventorshave found that such succinimide additives can efficiently reduce thecorrosion effects induced by amine-based and/or sulfur-based antiwearadditives.

Thus, the addition of at least one succinimide compound canadvantageously improve the anticorrosion properties of a lubricantcomposition comprising one or more amine-based and/or sulfur-basedantiwear additives.

For the purposes of the present invention, the term “anticorrosionadditive” denotes an additive for preventing or reducing the corrosionof metal parts. An anticorrosion additive used in a composition thusmakes it possible to improve the “anticorrosion” properties of saidcomposition.

The use of one or more succinimide compounds according to the inventiontogether with one or more amine-based and/or sulfur-based antiwearadditives advantageously affords access to a lubricant composition whichsimultaneously has good antiwear performance, while at the same timeovercoming the corrosion problems mentioned previously. A compositionaccording to the invention thus simultaneously has good antiwear andanticorrosion properties.

The corrosive (or corroding) power of a compound may be evaluated bymeans of a test involving study of the variation in the electricalresistance value of a copper wire of a preestablished diameter, as afunction of the duration of immersion of this wire in a compositioncomprising said test compound in a noncorrosive medium, for example inone or more base oils. The variation in this electrical resistance valueis directly correlated with the variation in the diameter of the testwire. Thus, in the context of the present invention, a compound istermed “noncorrosive” when the loss of diameter of the copper wirestudied is less than or equal to 1.3 μm after immersion for 80 hours, inparticular less than or equal to 0.8 μm after immersion for 40 hours inthe composition comprising said compound.

The dielectric properties of a lubricant are notably represented by theelectrical resistivity and the dielectric loss (tan δ) and may bemeasured according to the standard IEC 60247. The electrical resistivityrepresents the capacity of a material to oppose the circulation of anelectric current. It is expressed in ohm-metres (Ω.m). The resistivitymust not be low to prevent electrical conduction.

The electric dissipation factor or the loss angle tangent. The lossangle δ is the complementary angle of the phase shift between theapplied voltage and the alternating current. This factor reflects theJoule-effect energy losses. Heating is thus directly linked to the δvalue. A transmission oil typically has a tan δ value of the order ofunity at ambient temperature. A good insulating lubricant must maintaina low tan δ level.

Advantageously, the succinimide compound used according to the inventionis chosen from polyalkylene mono- or bis-succinimides, such aspolyisobutene (PIB) mono- or bis-succinimides; borate derivativesthereof; succinic anhydride derivatives thereof such as polyisobutylenesuccinic anhydrides (PIBSA); compounds obtained by opening such asuccinic anhydride ring, such as PIB pentaerythritol ester succinimides;and mixtures thereof.

Preferably, the succinimide compound is chosen from:

-   -   polyalkylene bis-succinimides in which the alkyl chain is        optionally linked to the succinimide via a —(C═CH₂)—group, in        particular polyisobutylene (PIB) bis-succinimides in which the        alkyl chain is optionally linked to the succinimide via a        —(C═CH₂)—group, and borate derivatives thereof, the two        succinimide groups being linked together by their respective        nitrogen atom via an alkylene group or a polyamine group, in        particular polyalkyleneamine;    -   polyalkylene mono-succinimides in which the alkyl chain is        optionally linked to the succinimide via a —(C═CH₂)—group, in        particular polyisobutylene (PM) mono-succinimides in which the        alkyl chain is optionally linked to the succinimide via a        —(C═CH₂)—group, and borate derivatives thereof, substituted on        the nitrogen atom with a polyamine group, in particular        polyalkyleneamine; and    -   mixtures thereof.

The introduction, into a lubricant composition intended for a propulsionsystem of an electric or hybrid vehicle, of one or more succinimidecompounds according to the invention thus advantageously permits theuse, in the composition, of amine-based and/or sulfur-based antiwearadditives, such as dimercaptothiadiazoles, without, however, entailingan adverse corrosive effect.

The amine-based and/or sulfur-based antiwear additives used in alubricant composition according to the invention are more particularlydetailed in the text hereinbelow, They are preferably chosen fromamine-based and sulfur-based antiwear additives. They may preferably bethia(di)azole compounds, in particular dimercaptothiadiazolederivatives.

In addition, a composition that is suitable for use in the invention hasthe advantage of being easy to formulate. Besides good antiwear andanticorrosion performance, it has good stability, notably with respectto oxidation, and also good properties in terms of electricalinsulation.

The present invention also relates to the use, for lubricating apropulsion system of an electric or hybrid vehicle, in particular forlubricating the electric motor and the power electronics of an electricor hybrid vehicle, of a lubricant composition comprising:

-   -   one or more succinimide compounds as defined in the invention,        as anticorrosion additives); and    -   one or more amine-based and/or sulfur-based antiwear additives        as defined in the invention.

A subject of the present invention is also a process for lubricating a.propulsion system of an electric or hybrid vehicle, comprising at leastone step of placing at least one mechanical part of said system incontact with a lubricant composition comprising at least one succinimidecompound as defined in the invention, as anticorrosion additive and atleast one amine-based and/or sulfur-based antiwear additive as definedin the invention.

Advantageously, a lubricant composition according to the invention isused for lubricating the electric motor itself, in particular therolling bearings located between the rotor and the stator of an electricmotor, and/or the transmission, in particular the reducer, in anelectric or hybrid vehicle.

Other features, variants and advantages of the use of succinimidecompounds as anticorrosion additives according to the invention willemerge more clearly on reading the description and the examples thatfollow, which are given as nonlimiting illustrations of the invention.

In the continuation of the text, the expressions “between . . . and . .. ”,“ranging from . . . to . . . ” and “varying from . . . to . . .” areequivalent and are intended to mean that the limits are included, unlessotherwise mentioned,

Unless otherwise indicated, the expression “including a(n)” should beunderstood as “comprising at least one”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents a propulsion system of an electric orhybrid vehicle.

DETAILED DESCRIPTION Anticorrosion Additives of Succinimide Type

As stated previously, the additive used as anticorrosion agent accordingto the invention, together with one or more amine-based and/orsulfur-based antiwear additives, in a lubricant composition for thepowertrain system of an electric or hybrid vehicle, is a succinimidecompound.

As mentioned previously, many succinimide compounds have already beenproposed for their use as dispersants, for instance polyalkylene mono-or bis-succinimides, such as polyisobutene (PIB) mono- orbis-succinimides; borate derivatives thereof; succinic anhydridederivatives thereof, for instance polyisobutylene succinic anhydrides(PIBSA); compounds obtained by opening such a succinic anhydride ring,for instance polyisobutylene pentaerythritol ester succinimides.

However, as indicated previously, such compounds have never beenproposed as anticorrosion additives in a lubricant for the powertrainsystem of an electric or hybrid vehicle, for the purposes of reducing oreven inhibiting the corrosion effects induced by the use of one or moreamine-based and/or sulfur-based antiwear additives.

Succinimide compounds are compounds comprising at least one succinimidegroup, in other words a group of formula (i) below:

or a borate derivative (B—O bond) thereof; or a succinic anhydridederivative of such a succinimide group, or a compound obtained byopening of the succinic anhydride ring.

As already mentioned previously, succinimide compounds may be of diversenature. They may be mono-succinimide or bis-succinimide compounds.

Preferably, the succinimide compound is chosen from compounds comprisingat least one substituted succinimide group, in particular of formula(ii) below:

or a borate derivative (B—O bond) of such a substituted succinimidegroup of formula (ii); or a succinic anhydride derivative of such asubstituted succinimide group of formula (ii), or a compound obtained byopening of the succinic anhydride ring,

-   -   in which R¹ represents a hydrocarbon-based group preferably        comprising from 8 to 400 carbon atoms.

R¹ may be chosen more particularly from linear or branched C₈ to C₄₀₀and in particular C₅₀ to C₂₀₀ alkyl groups, linear or branched C₈ toC₄₀₀ and in particular C₅₀ to C₂₀₀ alkenyl groups, C₆ to C₁₀ arylgroups, aryIalkyl groups and alkylaryl groups.

Preferably, R¹ represents a long C₈ to C₄₀₀ and in particular C₅₀ toC₂₀₀ alkyl chain, which is preferably branched, or a long C₈ to C₄₀₀ andin particular C₅₀ to C₂₀₀ alkenyl chain, which is preferably branched,including only one double bond, of which one of the two carbon atoms isdirectly linked to the succinimide ring.

Advantageously, R¹ represents a polyalkylene group, preferably having amass-average molecular mass Mw of between 140 and 50 000, in particularbetween 2000 and 30 000. According to a particular embodiment, R¹represents a polyisobutylene group, preferably with a number-averagemolecular mass of between 140 and 30 000, in particular between 2000 and20 000, or even between 2000 and 7000 and notably between 3000 and 5000.

According to another particular embodiment, R¹ represents apolyisobutylene group, preferably with a number-average molecular massof between 140 and 30 000, in particular between 2000 and 20 000, oreven between 2000 and 7000 and notably between 3000 and 5000, linked tothe succinimide group via a —(C═CH₂)—group and is of formula (A) below:

-   -   in which the symbol * indicates the point of attachment of this        group to the succinimide group, and n represents an integer        ranging from 6 to 500.

Thus, according to a particular embodiment, the succinimide compoundcomprises at least one substituted succinimide group of formula (ii), ora borate derivative of said group (ii), or a succinic anhydridederivative of said group (ii), or a compound obtained by opening of thesuccinic anhydride ring,

-   -   in which R¹ represents a hydrocarbon-based group, preferably        comprising from 8 to 400 carbon atoms, in particular a        polyalkene group optionally linked to the succinimide group via        a —(C═CH₂)—group, preferably having a mass-average molecular        mass Mw of between 140 and 50 000, in particular between 2000        and 30 000, and more particularly a polyisobutylene group        optionally linked to the succinimide group via a —(C═CH₂)—group,        preferably with a mass-average molecular mass Mw of between 140        and 30 000, in particular between 2000 and 20 000 or even        between 2000 and 7000 and notably between 3000 and 5000.

More particularly, the succinimide compound may be chosen frommono-succinimide compounds comprising a substituted succinimide group ofthe abovementioned formula (ii) and bis-succinimide compounds comprisingtwo substituted succinimide groups, in particular of the abovementionedformula (ii), said succinimide groups being more particularly connectedat their apex bearing a nitrogen atom with a polyamine group,

According to a particular embodiment, the succinimide compound usedaccording to the invention corresponds to formula (I) below:

or a borate derivative thereof,

-   -   in which A represents a linear or branched C₂ to C₂₄ and        preferably C₂ to C₆ alkylene group;    -   R¹ is as defined previously, for example a polyisobutylene group        optionally linked to the succinimide group via a —(C═CH₂)—group;    -   x represents 0 or an integer ranging from 1 to 6; preferably, x        is equal to 2, 3 or 4;    -   R² and R³ are chosen, independently of each other, from a        hydrogen atom, a linear or branched alkyl group, notably of C₁        to C_(25,) an alkoxy group, notably of C₁ to C_(12,) an alkenyl        group, in particular of C₂ to C_(12,) optionally bearing one or        more hydroxyl and/or amine functions,    -   or R² and R³ form, together with the nitrogen atom which bears        them, an optionally substituted succinimide group, preferably a        succinimide group substituted with a group R¹ as defined above.

According to a first embodiment variant, a succinimide compound usedaccording to the invention may be a mono-succinimide compound of theabovementioned formula (I) in which R² and R³ are chosen, independentlyof each other, from a hydrogen atom, a linear or branched alkyl group,notably of C₁ to C_(25;) an alkoxy group, notably of C₁ to C_(12,) analkenyl group, in particular of C₂ to C_(12,) optionally bearing one ormore hydroxyl and/or amine functions.

Preferably, a succinimide compound used according to the invention is ofthe abovementioned formula (I) in which R² and R³ represent hydrogenatoms.

In other words, a succinimide compound used according to the inventionmay be of formula (II) below:

or a borate derivative thereof,

-   -   in which: R¹ is as defined previously; in particular, R¹        represents a polyalkylene group optionally linked to the        succinimide group via a —(C═CH₂)—group, in particular        polyisobutylene optionally linked to the succinimide group via a        —(C═CH₂)—group,    -   A is as defined previously, and preferably represents at least        one of the following segments: —CH₂—CH₂—,        —CH₂—CH₂—CH₂—,—CH₂—CH(CH₃)—; and    -   y represents an integer between 1 and 6; in particular, y        represents 2, 3 or 4,

According to another embodiment variant, a succinimide compound usedaccording to the invention may be a bis-succinimide compound of theabovementioned formula (I) in which R² and R³ form, together with thenitrogen atom which bears them, an optionally substituted succinimidegroup, preferably a succinimide group substituted with a group R¹ asdefined above.

Advantageously, a bis-succinimide compound used according to theinvention may be of formula (III) below:

or a borate derivative thereof, in which:

-   -   R¹, which may be identical or different, are as defined        previously;    -   z represents an integer between 0 and 10 and preferably between        2 and 6;    -   s represents an integer between 2 and 6 and preferably between 2        and 4.

Preferably, the bis-succinimide compound may be of formula (III) inwhich R¹ represents polyalkylene groups, in particular polyisobutylenegroups, preferably with a molecular mass of between 150 and 15 000, inparticular between 500 and 2000 and notably between 500 and 1500.

The borate derivatives of the succinimide compounds of theabovementioned formula (I), (II) or (III) may be obtained from thenon-borate succinimide compounds by reaction with borates, for examplewith boric acid, in particular to reach a concentration of from 0.1% to3% by mass and notably from 1% to 2% by mass of boron in the succinimidecompound.

Among the succinic anhydride derivatives that are suitable for use inthe invention, mention may be made of polyisoalkylene succinicanhydrides, in particular polyisobutylene succinic anhydrides (known asPIBSA) such as the following compound, with a number-average molecularmass Mn of between 300 and 30 000 and a mass-average molecular mass Mwof between 300 and 30 000:

in which R is a polyisobutylene group.

Among the compounds obtained by opening the succinic anhydride ring,mention may notably be made of polyalkylene pentaerythritol estersuccinimides, for instance polyisobutylenes pentaerythritol estersuccinimides having the following formulae, with a number-averagemolecular mass Mn of between 300 and 30 000 and a mass-average molecularmass Mw of between 300 and 30 000:

in which PIB represents a polyisobutylene;

in which PIB represents a polyisobutylene.

In the context of the invention, the following definitions apply:

-   “alkyl”: a linear or branched, saturated aliphatic group; for    example, a Cx to Cz alkyl represents a linear or branched    hydrocarbon-based chain of x to z carbon atoms;-   “alkylene” represents a divalent alkyl group. For example, a    C_(x)-C_(z) alkylene group represents a linear or branched divalent    hydrocarbon-based chain of x to z carbon atoms;-   “alkenyl”: a linear or branched, unsaturated aliphatic group; for    example, a Cx to Cz alkenyl group represents a linear or branched    unsaturated carbon-based chain of x to z carbon atoms; “alkoxy”: a    radical —O-alkyl, in which the alkyl group is as defined previously;    “aryl”: a monocyclic or polycyclic aromatic group in particular    comprising between 5 and 10 carbon atoms. Examples of aryl groups    that may be mentioned include phenyl, tolyl and naphthyl groups.

Advantageously, the additive of succinimide type (mono-succinimide orbis-succinimide) is chosen from polyalkylene succinimides (in otherwords compounds comprising at least one group of the abovementionedformula (ii) in which R¹ is a polyalkylene group optionally linked tothe succinimide group via a —(C═CH₂)—group and notably polyisobutylene(PIB) succinimides in which the polyisobutylene part is optionallylinked to the succinimide group via a —(C═CH₂)—group, and boratederivatives thereof.

According to a particular embodiment, the additive of succinimide typeis chosen from polyalkylene succinimides in which the alkyl chain isoptionally linked to the succinimide via a —(C═CH₂)—group, in particularpolyisobutylene (PIB) succinimides in which the alkyl chain isoptionally linked to the succinimide via a —(C═CH₂)—group, and boratederivatives thereof, substituted on the nitrogen atom with a polyaminegroup, in particular polyalkyleneamine, for example polyethyleneamine.

Preferably, the additive of succinimide type is chosen frommono-succinimides or bis-succinimides of the abovementioned formula (I),in particular the mono-succinimides of the abovementioned formula (II),the bis-succinimides of the abovementioned formula (III), and mixturesthereof.

According to a particularly preferred embodiment, the additive ofsuccinimide type is chosen from:

-   -   polyalkylene bis-succinimides in which the alkyl chain is        optionally linked to the succinimide via a —(C═CH₂)—group, in        particular polyisobutylene (PIB) bis-succinimides in which the        alkyl chain is optionally linked to the succinimide via a        —(C═CH₂)—group, and borate derivatives thereof, the two        succinimide groups being linked together by their respective        nitrogen atom via an alkylene group or a polyamine group, in        particular polyalkyleneamine, or even polyethyleneamine;    -   polyalkylene mono-succinimides in which the alkyl chain is        optionally linked to the succinimide via a —(C═CH₂)—group, in        particular polyisobutylene (PIB) mono-succinimides in which the        alkyl chain is optionally linked to the succinimide via a        —(C═CH₂)—group, and borate derivatives thereof, substituted on        the nitrogen atom with a polyamine group, in particular        polyalkyleneamine, or even polyethyleneamine; and    -   mixtures thereof.

According to an even more particularly preferred embodiment, theadditive of succinimide type is chosen from the following compounds:

-   -   in which n ranges from 6 to 500 and is preferably 90; and R is a        linear or branched C₂ to C₂₄ and preferably C₂ to C₆ alkylene or        a group —R″—(NH-R′)x—in which R′ and R″ represent, independently        of each other, a linear or branched C₂ to C₂₄ and preferably C₂        to C₆ alkylene and x is an integer ranging from 1 to 6, and        preferably x is equal to 2, 3, 4 or 5. It is more precisely a        bis-succinimide for which the average molecular mass Mn is        between 3000 and 4000, and is preferably 3410; the average        molecular mass Mw is between 5000 and 6000, and is preferably        5225; the polydispersity index Ip is between 1.25 and 2, and is        preferably 1.5;

-   -   in which n ranges from 10 to 350 and is preferably 65; and R is        a linear or branched C₁ to C₂₄ and preferably C₂ to C₆ alkyl or        a group —(R′—(NH)y—H in which R′ represents a linear or branched        C₂ to C₂₄ and preferably C₂ to C₆ alkylene and y is an integer        ranging from 1 to 6, and preferably x is equal to 2, 3 or 4. It        is more precisely a PIB succinimide for which the average        molecular mass Mn is between 800 and 18 000, and is preferably        3519; the average molecular mass Mw is between 1000 and 20 000,        and is preferably 6220; the polydispersity index Ip is between        1.5 and 2.3, and is preferably 1.6; and    -   mixtures thereof.

It is understood that, in the context of the present invention, asuccinimide compound under consideration according to the invention maybe in the form of a mixture of at least two succinimide compounds, inparticular as defined previously.

The succinimide compounds used according to the invention may becommercially available or prepared according to synthetic methods knownto those skilled in the art.

For example, succinimide compounds may be synthesized by condensation ofan optionally substituted succinic anhydride, for example of a succinicanhydride substituted with a polyisobutylene group, with apoly(alkyleneamine). The succinic anhydride substituted with apolyisobutylene group (PIB) may be obtained beforehand, for example byreaction of maleic anhydride with methylvinylidene polyisobutene.

The invention is not limited to the succinimide compounds specificallydescribed above.

Other succinimide compounds, notably known as dispersants, may be usedas anticorrosion additives according to the invention.

The succinimide compound(s), in particular as defined previously, may beused in a lubricant composition according to the invention in aproportion of from 0.01% to 10% by mass, in particular from 0.1% to 10%by mass and more particularly from 0.5% to 8% by mass relative to thetotal mass of the lubricant composition.

Advantageously, a lubricant composition under consideration according tothe invention does not comprise any anticorrosion additives other thanthe succinimide compounds.

According to a particular embodiment, a lubricant composition usedaccording to the invention is free of anticorrosion additives oftriazole type or of the type such as compounds bearing an amine functionor a sterically hindered phenol function.

Lubricant Composition

Amine-Based and/or Sulfur-Based Antiwear Additives

As indicated previously, a lubricant composition under considerationaccording to the invention comprises one or more amine-based and/orsulfur-based antiwear additives.

The term “amine-based and/or sulfur-based antiwear additive” denotes anadditive chosen from amine-based antiwear additives, sulfur-basedantiwear additives and amine-based and sulfur-based antiwear additives.

The term “antiwear additive” denotes a compound which, when used in alubricant composition, notably a lubricant composition for a propulsionsystem of an electric or hybrid vehicle, makes it possible to improvethe antiwear properties of the composition.

The amine-based and/or sulfur-based antiwear additive may be chosen, forexample, from additives of thia(di)azole type, in particulardimercaptothiadiazole derivatives; polysulfide additives, notablysulfur-based olefins, amine phosphates, phospho-sulfur additives such asalkylthiophosphates, and mixtures thereof.

Thia(di)azole Additives

According to a particularly preferred embodiment, a lubricantcomposition under consideration according to the invention comprises atleast one thia(di)azole antiwear additive.

Thia(di)azole compounds are compounds which contain both a sulfur atomand at least one nitrogen atom in a five-atom ring. Benzothiazoles are aparticular type of thia(di)azoles. This term “thia(di)azole” includes,besides cyclic compounds containing one sulfur atom and one nitrogenatom per five-atom ring, also thiadiazoles which contain sulfur and twonitrogen atoms in such a ring.

In particular, the thia(di)azole compounds may be chosen frombenzothiazole derivatives, thiazole derivatives and thiadiazolederivatives.

Preferably, the antiwear additive may be a thiadiazole derivative.

Thiadiazoles are heterocyclic compounds comprising two nitrogen atoms,one sulfur atom, two carbon atoms and two double bonds, of generalformula C₂N₂SH_(2,) which may exist in the following forms,respectively: 1,2,3-thiadiazole; 1,2,4-thiadiazole; 1,2,5-thiadiazole;1,3,4-thiadiazole:

Preferably, the thiadiazole derivative is a dimercaptothiadiazolederivative.

Thus, according to a particularly preferred embodiment, a lubricantcomposition according to the invention comprises at least one antiwearadditive chosen from dimercaptothiazole derivatives.

The term “dimercaptothiadiazole derivative” according to the inventionmeans chemical compounds derived from the following fourdimercaptothiadiazole molecules below: 4,5-dimercapto-1,2,3-thiadiazole,3,5-dimercapto-1,2,4-thiadiazole, 3,4-dimercapto-1,2,5-thiadiazole,2,5-dimercapto-1,3,4-thiadiazole, taken alone or as a mixture:

The dimercaptothiadiazole derivatives are more particularly molecules ora mixture of molecules based on 4,5-dimercapto-1,2,3-thiadiazole,3,5-dimercapto-1,2,4-thiadiazole, 3,4-dimercapto-1,2,5-thiadiazole or2,5-dimercapto-3,4-thiadiazole, as represented above, in which at leastone of the substitutions=S, or even both substitutions=S on thethiadiazole ring is replaced with a substituent:

-   -   in which * represents the bond with a carbon atom of the        5-membered ring; n represents an integer equal to 1, 2, 3 or 4;        and R₁ is chosen from a hydrogen atom, a linear or branched,        saturated or unsaturated alkyl group comprising from1 to 24,        preferably from 2 to 18, more preferentially from 4 to 16 and        even more preferentially from 8 to 12 carbon atoms or an        aromatic substituent.

In particular, taking 2,5-dimercapto-1,3,4-thiadiazole as example, the2,5-dimercapto-1,3,4-thiadiazole derivatives are molecules having thefollowing formulae, taken alone or as a mixture:

-   -   in which the group(s) R₁ represent, independently of each other,        hydrogen atoms, linear or branched alkyl or alkenyl groups        comprising from 1 to 24, preferably from 2 to 18, more        preferentially from 4 to 16 and even more preferentially from 8        to 12 carbon atoms or aromatic substituents, n being,        independently of each other, integers equal to 1, 2, 3 or 4, n        preferably being equal to 1.

Preferably, R₁ represent, independently of each other, linear C₁ toC_(24,) preferably C₂ to C₁₈, notably C₄ to C_(16,) more particularly C₈to C₁₂ and preferably C₁₂ alkyl groups.

The dimercaptothiadiazole derivatives used in the present invention maybe commercially available, for example from the suppliers Vanderbilt,Rhein Chemie or Afton.

Polysulfide Additives

The amine-based and/or sulfur-based antiwear additive(s) used in alubricant composition according to the invention may also be chosen fromsulfur-based antiwear additives of polysulfide type, in particularsulfur-based olefins.

The sulfur-based olefins used in a lubricant composition according tothe invention may notably be dialkyl sulfides represented by the generalformula R_(a)—S_(x)—R_(b), in which R_(a) and R_(b) are alkyl groupsincluding from 3 to 15 carbon atoms, preferentially from 1 to 5 carbonatoms, preferentially 3 carbon atoms, and x is an integer between 2 and6.

Preferably, the polysulfide additive is chosen from dialkyl trisulfides.

Preferably, the antiwear additive present in a composition usedaccording to the invention is chosen from amine-based and sulfur-basedantiwear additives, and advantageously from thia(di)azole compounds asdescribed above and more preferentially from dimercaptothiadiazolederivatives.

A lubricant composition under consideration according to the inventionmay comprise from 0.01% to 10% by mass, in particular from 0.1% to 5% bymass and more particularly from 0.5% to 3% by mass of amine-based and/orsulfur-based antiwear additive(s), preferably of thia(di)azole type andmore preferentially chosen from dimercaptothiadiazole derivatives,relative to the total mass of the lubricant composition.

The use of other antiwear additives, notably known for lubricants forpropulsion systems, other than amine-based and/or sulfur-basedadditives, is envisageable, provided that they do not affect theproperties imparted by the combination of said succinimide compound(s)and of said amine-based and/or sulfur-based antiwear additive(s)according to the invention.

A lubricant composition under consideration according to the inventionmay comprise from 0.01% to 5% by mass, in particular from 0.1% to 10% bymass and more particularly from 0.5% to 5% by mass of antiwearadditive(s), including one or more amine-based and/or sulfur-basedadditives, as described previously.

Preferably, a lubricant composition required according to the inventionis free of antiwear additives other than said amine-based and/orsulfur-based antiwear additive(s) used according to the invention.

According to a particularly preferred embodiment, a lubricantcomposition under consideration according to the invention combines:

-   -   one or more succinimide compounds, in particular chosen from        polyalkylene mono-succinimides or bis-succinimides and borate        derivatives thereof, such as polyisobutene mono-succinimides or        bis-succinimides and borate derivatives thereof, in particular        chosen from the compounds of the abovementioned formula (I),        preferably from the compounds of formulae (II) and (III) as        defined above; and    -   one or more amine-based and sulfur-based antiwear additives,        preferably chosen from dimercaptothiazole derivatives, in        particular as defined above.

A composition used according to the invention may comprise, besides oneor more additives of succinimide type and one or more amine-based and/orsulfur-based antiwear additives, in particular as defined previously,one or more base oils, and also other additives, conventionallyconsidered in lubricant compositions.

Base Oil

A lubricant composition under consideration according to the inventionmay thus comprise one or more base oils.

These base oils may be chosen from the base oils conventionally used inthe field of lubricant oils, such as mineral, synthetic or natural,animal or plant oils or mixtures thereof.

It may be a mixture of several base oils, for example a mixture of two,three or four base oils.

The base oils of the lubricant compositions under considerationaccording to the invention may in particular be oils of mineral orsynthetic origin belonging to groups I to V according to the classesdefined in the API classification (or equivalents thereof according tothe ATIEL classification) and presented in Table 1 below or mixturesthereof.

TABLE 1 Content of Sulfur Viscosity saturates content index (VI) Group I<90% >0.03% 80 ≤ VI < 120 Mineral oils Group II ≥90% ≤0.03% 80 ≤ VI <120 Hydrocracked oils Group III ≥90% ≤0.03% ≥120 Hydrocracked orhydroisomerized oils Group IV Poly-α-olefins (PAO) Group V Esters andother bases not included in groups I to IV

The mineral base oils include all types of base oils obtained byatmospheric and vacuum distillation of crude oil, followed by refiningoperations such as solvent extraction, deasphalting, solventdeparaffinning, hydrotreating, hydrocracking, hydroisomerization andhydrofinishing.

Mixtures of synthetic and mineral oils, which may be biobased, may alsobe used. There is generally no limit as regards the use of differentbase oils for preparing the compositions used according to theinvention, other than the fact that they must have properties, notablyin terms of viscosity, viscosity index or resistance to oxidation, thatare suitable for use for the propulsion systems of an electric or hybridvehicle.

The base oils of the compositions used according to the invention mayalso be chosen from synthetic oils, such as certain esters of carboxylicacids and of alcohols, poly-α-olefins (PAO) and polyalkylene glycols(PAG) obtained by polymerization or copolymerization of alkylene oxidescomprising from 2 to 8 carbon atoms, in particular from 2 to 4 carbonatoms.

The PAOs used as base oils are obtained, for example, from monomerscomprising from 4 to 32 carbon atoms, for example from octene or decene.The weight-average molecular mass of the PAO may vary quite broadly.Preferably, the weight-average molecular mass of the PAO is less than600 Da. The weight-average molecular mass of the PAO may also range from100 to 600 Da, from 150 to 600 Da or from 200 to 600 Da.

Advantageously, the base oil(s) of the composition used according to theinvention are chosen from poly-α-olefins (PAO), polyalkylene glycols(PAG) and esters of carboxylic acids and of alcohols.

According to an alternative embodiment, the base oil(s) of thecomposition used according to the invention may be chosen from group IIor III base oils.

It falls to a person skilled in the art to adjust the content of baseoil to be used in a composition that is suitable for use in theinvention.

A lubricant composition under consideration according to the inventionmay comprise at least 50% by mass of base oil(s) relative to its totalmass, in particular from 60% to 99% by mass of base oil(s), relative toits total mass.

Additional Additives

A lubricant composition that is suitable for use in the invention mayalso comprise any type of additive, different from the additives ofsuccinimide type and from the amine-based and/or sulfur-based antiwearadditives defined in the context of the present invention, that aresuitable for use in a lubricant for a propulsion system of an electricor hybrid vehicle.

It is understood that the nature and amount of additives used are chosenso as not to affect the properties in terms of antiwear andanticorrosion performance imparted by the combination of saidsuccinimide compound(s) and of said amine-based and/or sulfur-basedadditive(s) used according to the invention.

Such additives, which are known to a person skilled in the art in thefield of the lubrication and/or cooling of the propulsion systems ofelectric or hybrid vehicles, may be chosen from friction modifiers,detergents, extreme-pressure additives, dispersants other than thesuccinimide compounds according to the invention, antioxidants, pourpoint depressants, antifoams and mixtures thereof.

Advantageously, a composition that is suitable for use in the inventioncomprises at least one additional additive chosen from frictionmodifiers, viscosity index modifiers, detergents, extreme-pressureadditives, dispersants, antioxidants, pour point depressants, antifoamsand mixtures thereof.

These additives may be introduced individually and/or in the form of amixture such as those already available for sale for commerciallubricant formulations for vehicle engines, with a performance level asdefined by the ACEA (Association des Constructeurs Européensd'Automobiles) and/or the API (American Petroleum Institute), which arewell known to those skilled in the art.

A lubricant composition that is suitable for use in the invention maycomprise at least one friction-modifying additive. Thefriction-modifying additive may be chosen from a compound providingmetal elements and an ash-free compound. Among the compounds providingmetal elements, mention may be made of complexes of transition metalssuch as Mo, Sb, Sn, Fe, Cu or Zn, the ligands of which may behydrocarbon-based compounds comprising oxygen, nitrogen, sulfur orphosphorus atoms. The ash-free friction-modifying additives aregenerally of organic origin and may be chosen from fatty acid monoestersof polyols, alkoxylated amines, alkoxylated fatty amines, fattyepoxides, borate fatty epoxides, fatty amines or fatty acid esters ofglycerol. According to the invention, the fatty compounds comprise atleast one hydrocarbon-based group comprising from 10 to 24 carbon atoms.

A lubricant composition that is suitable for use according to theinvention may comprise from 0.01% to 2% by weight or from 0.01% to 5% byweight, preferentially from 0.1% to 1.5% by weight or from 0.1% to 2% byweight of friction-modifying additive, relative to the total weight ofthe composition.

A lubricant composition used according to the invention may comprise atleast one antioxidant additive.

The antioxidant additive generally makes it possible to retard thedegradation of the composition in service. This degradation may notablybe reflected by the formation of deposits, the presence of sludges, orby an increase in the viscosity of the composition.

The antioxidant additives notably act as free-radical inhibitors orhydroperoxide destroyers. Among the commonly used antioxidant additives,mention may be made of antioxidant additives of phenolic type,antioxidant additives of amine type and phospho-sulfur-based antioxidantadditives. Some of these antioxidant additives, for example thephospho-sulfur-based antioxidant additives, may be ash generators. Thephenolic antioxidants additives may be ash-free or may be in the form ofneutral or basic metal salts. The antioxidants additives may notably bechosen from sterically hindered phenols, sterically hindered phenolesters and sterically hindered phenols comprising a thioether bridge,diphenylamines, diphenylamines substituted with at least one C₁-C₁₂alkyl group, N,N′-dialkyl-aryl-diamines, and mixtures thereof.

Preferably according to the invention, the sterically hindered phenolsare chosen from compounds comprising a phenol group, in which at leastone carbon vicinal to the carbon bearing the alcohol function issubstituted with at least one C₁-C₁₀ alkyl group, preferably a C₁-C₆alkyl group, preferably a C₄ alkyl group, preferably with a tert-butylgroup.

Amine compounds are another class of antioxidant additives that may beused, optionally in combination with the phenolic antioxidantsadditives. Examples of amine compounds are aromatic amines, for examplethe aromatic amines of formula NR⁴R⁵R⁶ in which R⁴ represents anoptionally substituted aliphatic or aromatic group, R⁵ represents anoptionally substituted aromatic group, R⁶ represents a hydrogen. atom,an alkyl group, an aryl group or a group of formula R⁷S(O)₂R⁸ in whichR⁷ represents an alkylene group or an alkenylene group, R⁸ represents analkyl group, an alkenyl group or an aryl group and z represents 0, 1 or2.

Sulfurized alkylphenols or the alkali metal and alkaline-earth metalsalts thereof may also be used as antioxidant additives.

Another class of antioxidant additives is that of copper compounds, forexample copper thio- or dithio-phosphates, copper salts of carboxylicacids, and copper dithiocarbamates, sulfonates, phenates andacetylacetonates. Copper I and II salts and succinic acid or anhydridesalts may also be used.

A lubricant composition used according to the invention may contain anytype of antioxidant additive known to those skilled in the art.

Advantageously, a lubricant composition used according to the inventioncomprises at least one ash-free antioxidant additive.

A lubricant composition used according to the invention may comprisefrom 0.5% to 2% by weight of at least one antioxidant additive, relativeto the total weight of the composition.

According to a particular embodiment, a lubricant composition usedaccording to the invention is free of antioxidant additives of aromaticamine type or of sterically hindered phenol type.

A lubricant composition that is suitable for use in the invention mayalso comprise at least one detergent additive.

The detergent additives generally make it possible to reduce theformation of deposits on the surface of metal parts by dissolving theoxidation and combustion byproducts.

The detergent additives that may be used in a lubricant composition usedaccording to the invention are generally known to those skilled in theart. The detergent additives may be anionic compounds comprising a longlipophilic hydrocarbon-based chain and a hydrophilic head. Theassociated cation may be a metal cation of an alkali metal or analkaline-earth metal.

The detergent additives are preferentially chosen from alkali metal oralkaline-earth metal salts of carboxylic acids, sulfonates, salicylatesand naphthenates, and also phenate salts. The alkali metals andalkaline-earth metals are preferentially calcium, magnesium, sodium orbarium.

These metal salts generally comprise the metal in a stoichiometricamount or in excess, thus in an amount greater than the stoichiometricamount. They are then overbased detergent additives; the excess metalgiving the overbased nature to the detergent additive is then generallyin the form of a metal salt that is insoluble in the oil, for example acarbonate, a hydroxide, an oxalate, an acetate or a glutamate,preferentially a carbonate.

A lubricant composition that is suitable for use in the invention maycomprise, for example, from 2% to 4% by weight of detergent additiverelative to the total weight of the composition.

Also, a lubricant composition used according to the invention maycomprise at least one dispersant, different from the succinimidecompounds defined according to the invention.

The dispersant may be chosen from Mannich bases.

A lubricant composition used according to the invention may comprise,for example, from 0.2% to 10% by weight of dispersant(s) different fromthe succinimide compounds defined according to the invention, relativeto the total weight of the composition.

Advantageously, the lubricant composition used according to theinvention does not comprise any dispersants different from thesuccinimide compounds defined according to the invention.

A lubricant composition that is suitable for use in the invention mayalso comprise at least one antifoam.

The antifoam may be chosen from silicones.

A lubricant composition that is suitable for use in the invention maycomprise from 0.01% to 2% by mass or from 0.01% to 5% by mass,preferentially from 0.1% to 1.5% by mass or from 0.1% to 2% by mass ofantifoam, relative to the total weight of the composition.

A lubricant composition that is suitable for use in the invention mayalso comprise at least one pour-point depressant (PPD).

By slowing down the formation of paraffin crystals, the pour-pointdepressant additives generally improve the cold-temperature behavior ofthe composition. Examples of pour-point depressant additives that may bementioned include polyalkyl methacrylates, polyacrylates,polyarylamides, polyaklphenols, polyalkylnaphthalenes andpolyalkylstyrenes.

In particular, a lubricant composition used according to the inventionmay be free of anticorrosion additive of triazole type and ofantioxidant additive of aromatic amine type or of sterically hinderedphenol type.

In terms of formulation of such a lubricant composition, saidsuccinimide compound(s) may be added to a base oil or mixture of baseoils, and the other additional additives, including the amine-basedand/or sulfur-based antiwear additive(s), are then added.

Alternatively, said succinimide compound(s) may be added to apre-existing conventional lubricant formulation, notably comprising oneor more base oils, one or more amine-based and/or sulfur-based antiwearadditives, and optionally additional additives.

Alternatively, said anticorrosion additive(s) of succinimide typeaccording to the invention may be combined with one or more additionaladditives, and the additive “pack” thus formed is added to a base oil ormixture of base oils.

Advantageously, a lubricant composition used according to the inventionhas a kinematic viscosity, measured at 100° C. according to the standardASTM D445, ranging from 1 to 15 mm²/s, in particular ranging from 3 to10 mm²/s.

Advantageously, a lubricant composition used according to the inventionhas a kinematic viscosity, measured at 40° C. according to the standardASTM D445, ranging from 3 to 80 mm²/s, in particular from 15 to 70mm²/s.

According to an advantageous embodiment of the present invention, theelectrical resistivity values measured at 90° C. for the lubricantcompositions used according to the invention are between 5 and 10 000Mohm.m, more preferably between 6 and 5000 Mohm.m.

According to an advantageous embodiment of the present invention, thedielectric loss values measured at 90° C. for the lubricant compositionsused according to the invention are between 0.01 and 30, more preferablybetween 0.02 and 25 and more preferentially between 0.02 and 10.

Advantageously, a lubricant composition used according to the inventionmay be of a grade according to the SAEJ300 classification defined by theformula (X)W(Y), in which X represents 0 or 5, and Y represents aninteger ranging from 4 to 20, in particular ranging from 4 to 16 or from4 to 12.

According to a particular embodiment, a lubricant composition usedaccording to the invention comprises, or even consists of:

-   a base oil or mixture of base oils, preferably chosen from    poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of    carboxylic acids and of alcohols;-   one or more additives of succinimide type, preferably chosen from    poly alkylene mono-succinimides and bis-succinimides, such as    polyisobutene mono-succinimides and bis-succinimides and borate    derivatives thereof, in particular chosen from the compounds of the    abovementioned formula (I), preferably from the compounds of    formulae (II) and (III) as defined above;-   one or more amine-based and/or sulfur-based antiwear additives,    preferably one or more amine-based and sulfur-based antiwear    additives, more preferentially chosen from compounds of    thia(di)azole type, in particular dimercaptothiazole derivatives as    defined above;-   optionally one or more additional additives chosen from friction    modifiers, viscosity index modifiers, detergents, extreme-pressure    additives, dispersants, antioxidants, pour point depressants,    antifoams and mixtures thereof.

According to a particular embodiment, a lubricant composition usedaccording to the invention comprises, or even consists of:

-   from 0.01% to 10% by mass, in particular from 0.1% to 10% by mass    and more particularly from 0.5% to 8% by mass of one or more    additives of succinimide type, preferably chosen from polyalkylene    mono-succinimides and bis-succinimides, such as polyisobutene    mono-succinimides and bis-succinimides and borate derivatives    thereof, in particular chosen from the compounds of the    abovementioned formula (I), preferably from the compounds of    formulae (II) and (III) as defined above;-   from 0.01% to 10% by mass, in particular from 0.1% to 5% by mass and    more particularly from 0.5% to 3% by mass one or more amine-based    and/or sulfur-based antiwear additives, preferably one or more    amine-based and sulfur-based antiwear additives, more preferentially    chosen from compounds of thia(di)azole type, in particular    dimercaptothiazole derivatives as defined above;-   from 60% to 99.9% by mass of base oil(s), preferably chosen from    poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of    carboxylic acids and of alcohols, and mixtures thereof;-   optionally from 0.1% to 5% by mass of one or more additives chosen    from friction modifiers, viscosity index modifiers, detergents,    extreme-pressure additives, dispersants, antioxidants, pour point    depressants, anti foams and mixtures thereof;-   the contents being expressed relative to the total mass of said    lubricant composition.

APPLICATION

As indicated previously, a lubricant composition that is suitable foruse in the invention as described previously is used as lubricant for apropulsion system of an electric or hybrid vehicle, and moreparticularly for the motor and the power electronics.

Thus, the present invention relates to the use of a lubricantcomposition as defined previously, combining one or more succinimidecompounds, in particular as defined previously, and one or moreamine-based and/or sulfur-based antiwear additives, preferablydimercaptothiazole derivatives, for lubricating a propulsion system ofan electric or hybrid vehicle, in particular for lubricating theelectric motor and the power electronics of an electric or hybridvehicle.

As represented schematically in FIG. 1, the propulsion system of anelectric or hybrid vehicle notably comprises the electric motor part(1), an electric battery (2) and a transmission, and in particular aspeed reducer (3).

The electric motor typically comprises power electronics (11) connectedto a stator (13) and a rotor (14). The stator comprises coils, inparticular copper coils, which are powered by an alternating electriccurrent. This makes it possible to generate a rotating magnetic field.For its part, the rotor comprises coils, permanent magnets or othermagnetic materials, and is placed in rotation by the rotating magneticfield.

A rolling bearing (12) is generally incorporated between the stator (13)and the rotor (14). A transmission, and in particular a speed reducer(3), makes it possible to reduce the rotation speed at the outlet of theelectric motor and to adapt the speed transmitted to the wheels, makingit possible simultaneously to control the speed of the vehicle.

The rolling bearing (12) is notably subjected to high mechanicalstresses and poses problems of wear by fatigue. It is thus necessary tolubricate the rolling bearing in order to increase its service life.Also, the reducer is subject to high friction stresses and thus needs tobe appropriately lubricated in order to prevent it from being damagedtoo quickly.

Thus, the invention relates in particular to the use of a composition asdescribed previously for lubricating an electric motor of an electric orhybrid vehicle, in particular for lubricating the rolling bearingslocated between the rotor and the stator of an electric motor.

The invention also relates to the use of a composition as describedpreviously for lubricating the transmission, in particular the reducer,in an electric or hybrid vehicle.

Advantageously, a composition according to the invention may thus beused for lubricating the various parts of a propulsion system of anelectric or hybrid vehicle, in particular the rolling bearings locatedbetween the rotor and the stator of an electric motor, and/or thetransmission, in particular the reducer, in an electric or hybridvehicle.

Advantageously, as mentioned previously, a lubricant compositionaccording to the invention has excellent antiwear and anticorrosionperformance,

According to another of its aspects, the invention also relates to aprocess for lubricating at least one part of a propulsion system of anelectric or hybrid vehicle, in particular the rolling bearings locatedbetween the rotor and the stator of an electric motor; and/or thetransmission, notably the reducer, comprising at least one step ofplacing at least said part in contact with a composition as describedpreviously.

The present invention thus proposes a process for simultaneouslyreducing the wear and corrosion of at least one part of a propulsionsystem of an electric or hybrid vehicle, in particular the rollingbearings located between the rotor and the stator of an electric motor;and/or the transmission, notably the reducer, said process comprising atleast one step of placing at least said part in contact with acomposition as described previously.

All of the features and preferences described for the composition usedaccording to the invention and for the uses thereof also apply to thisprocess.

According to a particular embodiment, a composition according to theinvention may have, besides lubricating properties, good electricalinsulation properties.

According to this embodiment, a composition according to the inventionmay simultaneously be used for lubricating one or more parts of apropulsion system of an electric or hybrid vehicle, in particular forlubricating the sensors and the solenoid valves of the motor, therolling bearings, but also the windings located in the rotor and thestator of an electric motor, or else for lubricating the transmission,in particular the gears, the sensors, the solenoid valves or the reducerwhich are found in an electric or hybrid vehicle, and for electricallyinsulating at least one part of said propulsion system, notably thebattery.

In the context of such an implementation variant, a lubricantcomposition under consideration according to the inventionadvantageously has a kinematic viscosity, measured at 100° C. accordingto the standard ASTM D445, of between 2 and 8 mm²/s, preferably between3 and 7 mm²/s.

It is understood that the uses described above may be combined, acomposition as described previously possibly being used both aslubricant and as electrical insulator, but also as coolant fluid for themotor, the battery and the transmission of an electric or hybridvehicle.

According to the invention, the particular, advantageous or preferredfeatures of the composition according to the invention make it possibleto define uses according to the invention that are also particular,advantageous or preferred.

The invention will now be described by means of the examples thatfollow, which are, needless to say, given as nonlimiting illustrationsof the invention.

Example

Various compositions were evaluated:

-   a composition C1 comprising an amine-based and sulfur-based antiwear    additive of dimercaptothiadiazole type free of additive of    succinimide type;-   a composition C2 comprising said antiwear additive of    dimercaptothiadiazole type and a dispersant additive of succinimide    type, in accordance with the invention, more precisely a    bis-succinimide having the following formula:

as defined previously,

-   a composition C3 comprising said antiwear additive of    dimercaptothiadiazole type and a dispersant additive of succinimide    type, in accordance with the invention, more precisely a high    molecular weight PIB succinimide,-   a composition C4 comprising said antiwear additive of    dimercaptothiadiazole type and a dispersant additive of succinimide    type, in accordance with the invention, more precisely a PIB    succinimide having the following formula:

as defined previously.

Compositions C1 to C4 comprise, besides the abovementioned compounds, agroup V base oil.

The compositions and the amounts (expressed as mass percentages) areindicated in Table 2 below.

TABLE 2 C1 C2 C3 C4 Base oil 99% 98% 98% 98% Dimercaptothiadiazole  1% 1%  1%  1% antiwear agent Bis-succinimide —  1% — — PIB-succinimide — — 1% — PIB-succinimide — — —  1%

EVALUATION OF THE ANTICORROSION PROPERTIES

Evaluation Method

The corrosive (or corroding) power of a composition may be evaluated bymeans of a test involving study of the variation in the electricalresistance value of a copper wire of a preestablished diameter, as afunction of the duration of immersion of this wire in the composition.The variation in this electrical resistance value is directly correlatedwith the variation in the diameter of the test wire. In the context ofthe present invention, the diameter of the wire chosen is 70 μm.

In the present case, a copper wire is immersed in a test tube containing20 mL of a test composition (compositions C2 to C4 being compositionsaccording to the invention and composition C1 being a compositionserving as a comparative).

The resistance of the wire is measured using an ohmmeter.

The measuring current is 1 mA.

The temperature of the test composition is brought to 150° C.

The resistance of the copper wire is calculated by this equation (1):

$\begin{matrix}{R = {\rho \times \frac{L}{S}}} & \left\lbrack {{Math}1} \right\rbrack\end{matrix}$

in which R is the resistance, ρis the resistivity of copper, L is thelength of the wire and S is the cross-sectional area.

In this equation (1), ρ and L are constants. Thus, the resistance R isinversely proportional to the cross-sectional area of the immersed wire.

The diameter of the wire is calculated from the cross-sectional area(equation (2)):

$\begin{matrix}{S = {\frac{\pi}{4} \times D^{2}}} & \left\lbrack {{Math}2} \right\rbrack\end{matrix}$

in which D is the diameter of the wire.

Equation (2) is inserted into equation (1) to obtain the relationshipbetween the resistance and the diameter (equation (3)):

$\begin{matrix}{R = {\rho \times \frac{L}{\frac{\pi}{4} \times D^{2}}}} & \left\lbrack {{Math}3} \right\rbrack\end{matrix}$

Thus, when the wire is corroded by the test compositions, the diameterof the wire decreases, thus bringing about an increase in the resistancevalue.

By monitoring the resistance, it is possible to monitor the change inthe diameter of the wire, which reflects the state of corrosion sufferedby the immersed wire.

The loss of diameter of the wire is thus calculated directly from themeasured resistance. When the measured resistance is infinite, this isan open circuit. The wire has thus broken, which defines very severecorrosion.

Results

The results are summarized in the following table and are expressed inμm (loss of diameter). The lower the value obtained, the better theanticorrosion properties of the composition evaluated.

A composition is considered to be “noncorrosive” when the loss ofdiameter of the copper wire studied is less than or equal to 1.3 μmafter immersion for 80 hours, in particular less than or equal to 0.8 μmafter immersion for 40 hours in the composition comprising saidcompound.

TABLE 3 Compositions C1 C2 C3 C4 Loss of diameter 0.28 0.55 0.44 0 (μm)at 20 hours Loss of diameter Broken wire 0.74 0.73 0.47 (μm) at 40 hoursLoss of diameter Broken wire 0.70 1.03 0.82 (μm) at 60 hours Loss ofdiameter Broken wire 0.82 1.28 1.19 (μm) at 80 hours

It emerges from these results that the addition of a succinimidecompound according to the invention makes it possible to reduce thecorrosion effects induced by the amine-based and sulfur-based antiwearadditive.

1-10. (canceled)
 11. A method or improving the anti-corrosion propertiesof a lubricant composition for a propulsion system of an electric orhybrid vehicle, comprising: adding at least one succinimide compound toa lubricant composition for lubricating the propulsion system, thelubricant composition comprising an amine-based anti-wear additiveand/or a sulfur-based anti-wear additive.
 12. The method of claim 11,wherein the at least one succinimide compound is chosen frompolyalkylene mono- or bis-succinimides; borate derivatives ofpolyalkylene mono- or bis-succinimides; succinic anhydride derivativesof polyalkylene mono- or bis-succinim ides; compounds obtained byopening such a succinic anhydride ring; or a combination thereof. 13.The method of claim 11, wherein the at least one succinimide compound ischosen from: polyisobutene (PIB) mono- or bis-succinim ides; boratederivatives of polyisobutene (PIB) mono- or bis-succinimides;polyisobutylene succinic anhydrides (PIBSA); polyisobutylenepentaerythritol ester succinimides; or a combination thereof.
 14. Themethod of claim 11, wherein the at least one succinimide compoundcomprises at least one substituted succinimide group of formula (ii)below:

borate derivatives of formula (ii), succinic anhydride derivatives offormula (ii), or a compound obtained by opening of the succinicanhydride ring of formula (ii), wherein R¹ represents ahydrocarbon-based group comprising from 8 to 400 carbon atoms.
 15. Themethod of claim 14, wherein R¹ represents a polyalkene group optionallylinked to the succinimide group via a —(C═CH₂)—group and having amass-average molecular mass Mw of between 2000 and 30,000.
 16. Themethod of claim 14, wherein R¹ represents a polyisobutylene groupoptionally linked to the succinimide group via a —(C═CH₂)—group andhaving a mass-average molecular mass Mw of between 2000 and
 7000. 17.The method of claim 11, wherein the at least one succinimide compound isa mono-succinimide of formula (II) below:

or a borate derivative thereof, wherein: R¹ represents a polyalkylenegroup optionally linked to the succinimide group via a —(C═CH₂)—group; Arepresents a linear or branched C₂ to C₆ alkylene group; and yrepresents an integer ranging from 2 to
 5. 18. The method of claim 17,wherein: R¹ represents a polyisobutylene group optionally linked to thesuccinimide group via a —(C═CH₂)—group; A represents at least one of thefollowing segments: —CH₂—CH₂—, —CH₂—CH₂—CH₂—, —CH₂—CH(CH₃)—; and yrepresents 2, 3, or
 4. 19. The method of claim 11, wherein the at leastone succinimide compound is a bis-succinimide of formula (III) below:

or a borate derivative thereof, wherein: R¹ represents polyalkylenegroups optionally linked to the succinimide group via a —(C═CH₂)—group;z represents an integer ranging from 1 to 10; and s represents aninteger ranging from 2 to
 6. 20. The method of claim 19, wherein: R¹represents polyisobutylene groups optionally linked to the succinimidegroup via a —(C═CH₂)—group; z represents an integer ranging from 2 to 6;and s represents an integer ranging from 2 to
 4. 21. The method of claim11, wherein the amine-based anti-wear additive and/or the sulfur-basedanti-wear additive is chosen from 2,5-dimercapto-1,3,4-thiadiazolederivatives having the following formulae, taken alone or as a mixture:

wherein: each R₁ group is independently selected from a hydrogen atom, alinear or branched alkyl or alkenyl group comprising from 2 to 18 carbonatoms, or an aromatic substituent; and each n is independently selectedfrom 1, 2, 3, or
 4. 22. The method of claim 21, wherein: each R₁ groupis independently selected from a hydrogen atom or linear or branchedalkyl or alkenyl groups comprising from 8 to 12 carbon atoms or aromaticsubstituents; and n is
 1. 23. The method of claim 11, wherein: the atleast one succinimide compound is present in an amount ranging from 0.1%to 10% by mass, relative to the total mass of the lubricant composition;and the amine-based anti-wear additive and/or the sulfur-based anti-wearadditive is present in an amount ranging from 0.01% to 10% by mass,relative to the total mass of the lubricant composition.
 24. The methodof claim 23, wherein: the at least one succinimide compound is presentin an amount ranging from 0.5% to 8% by mass, relative to the total massof the lubricant composition; and the amine-based anti-wear additiveand/or the sulfur-based anti-wear additive is present in an amountranging from 0.5% to 3% by mass, relative to the total mass of thelubricant composition.
 25. A method of reducing corrosion in apropulsion system of an electric or hybrid vehicle, the methodcomprising lubricating an electric motor and/or power electronics of theelectric or hybrid vehicle with a lubricant composition comprising: atleast one succinimide compound; and an amine-based anti-wear additiveand/or a sulfur-based anti-wear additive.
 26. The method of claim 25,wherein: at least one succinimide compound is chosen from: polyisobutene(PIB) mono- or bis-succinimides; borate derivatives of polyisobutene(PIB) mono- or bis-succinimides; polyisobutylene succinic anhydrides(PIBSA); polyisobutylene pentaerythritol ester succinim ides; or acombination thereof; and the amine-based anti-wear additive and/or thesulfur-based anti-wear additive is a 2,5-dimercapto-1,3,4-thiadiazolederivative.
 27. The method of claim 25, further comprising lubricatingrolling bearings located between a rotor and a stator of the electricmotor with the lubricant composition.
 28. The method of claim 25,further comprising lubricating a transmission of the electric or hybridvehicle with the lubricant composition.